Usage of radio spectrum, or spectrum for short, is regulated independently within different countries, or regions. An authority regulating spectrum usage in a certain region may be referred to as a regulator. Radio communication systems, such as cellular telecommunication systems, are developed and designed for different spectrum ranges, or operating bands. An operating band may be referred to as an operating frequency band.
An operating frequency band supports a specific duplex mode of operation. The possible duplex modes are frequency division duplex (FDD), time division duplex (TDD) and half duplex FDD (HD-FDD). In FDD mode of operation, which is used in Universal Terrestrial Radio Access Networks (UTRAN) FDD and Evolved Universal Terrestrial Radio Access Networks (E-UTRAN) FDD, the uplink and downlink transmission take place on different carrier frequencies. Reference is made to Third Generation Partnership Project (3GPP) TS 25.101, “User Equipment (UE) radio transmission and reception (FDD)”, 3GPP TS 25.104, “Base station (BS) radio transmission and reception (FDD)”, and 3GPP TS 36.101, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); User Equipment (UE) radio transmission and reception” and 3GPP TS 36.104, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); Base station (BS) radio transmission and reception”. Therefore, in FDD mode both uplink and downlink transmission can occur simultaneously in time. Carrier frequencies used, by a radio transceiver, in the uplink and the downlink are referred to as pass band for uplink and downlink, respectively. The minimum distance in frequency between the uplink and downlink pass bands is referred to as a duplex gap. The distance in frequency between the uplink and downlink carrier frequencies is referred to transmit-receive (TX-RX) frequency separation for the radio transceiver. The TX-RX frequency separation can be fixed, aka default, or variable. In the latter case the TX-RX frequency separation is configurable by the network.
On the other hand in TDD mode, which is used in UTRAN TDD and E-UTRAN TDD, the uplink and downlink transmission take place on the same carrier frequency channel but in different time slots or sub-frames. Reference is made to 3GPP TS 25.102, “User Equipment (UE) radio transmission and reception (TDD)”, 3GPP TS 25.105 “Base Station (BS) radio transmission and reception (TDD)”, 3GPP TS 36.101, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); User Equipment (UE) radio transmission and reception”, 3GPP TS 36.104, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); Base station (BS) radio transmission and reception”.
HD-FDD, which is used in Global System for Mobile Communications (GSM), can be regarded as a hybrid scheme where the uplink and downlink are transmitted on different carrier frequencies and are also transmitted on different time slots. Reference is made to 3GPP TS 05.05, “Radio Transmission and Reception”. This means uplink and downlink transmission do not occur simultaneously in time.
Returning to spectrum usage, one of the objectives of standardizing spectrum usage is to develop an operating band which can, preferably, be used globally. A global operating band leads to several advantages in terms of global roaming, reduced cost of the products due to the economy of scale, simplicity in building products/devices since the same or at least limited platforms/devices can be reused globally or regionally etc. However certain country specific and even operator specific frequency bands are unavoidable due to the fact that the spectrum availability for the mobile services may be fragmented in different country and even within a country. Furthermore, the regulators in each country independently allocate the frequency band in accordance with the available spectrum. Also the spectrum below 1 GHz due to its favourable propagation characteristics might be scarce or fragmented due to higher demand by other competing technologies. Additionally already existing services in a frequency band may be difficult to move or deprecate which makes certain frequencies available at different times. The assigned spectrum is eventually standardized in 3GPP in terms of frequency bands so that vendors can develop the products e.g. BS (base stations) and UE. Hence there might be a frequency band that is completely allocated in one region while a different region just allocates part of it. For example, Band 28, was initially allocated in the APAC region, the band is specified for FDD as 703-748 MHz for uplink (UL) and 758-803 MHz for downlink (DL). Some specific regions, as Japan will also deploy this band. However, not the complete spectrum can be allocated to International Mobile Telecommunications (IMT) but only 718-748 MHz/783-803 MHz. At the same time, Europe is also considering this spectrum and a part of the band may become available for wideband services.
UE roaming between different regions is a driver for making spectrum globally harmonized. From this perspective, the same UE can operate on a specific operating band in different regions even if the allocations and regulatory conditions are slightly different.
Another objective of standardizing spectrum usage is to develop an operating band which can guarantee that radio emissions outside the operating band are below certain levels.
The radio emissions outside the operating band occurs due to that although a wireless device typically operates in a well-defined portion of the frequency band, emissions outside the operating band or channel bandwidth, and also outside its operating frequency band, are unavoidable. These emissions outside the BW or frequency band are often termed as out of band emissions, spurious emissions, unwanted emissions or Out Of Band (OOB) emissions. Human bodies are exposed to emissions (Radio Frequency, RF exposure) both inside and outside the BW and/or frequency band of operation.
These two concepts, i.e. OOB emission and RF exposure to human, and their associated signalling aspects are described below.
The UEs as well as base stations have to fulfil certain OOB emission requirements, aka spurious emission requirements. The objective of OOB emission requirements is to limit the interference caused by the transmitters, e.g. UE or BS, outside their respective channel bandwidths, i.e. carrier(s) on which transmission occur(s), to the adjacent carriers or carriers with a greater frequency separation. In fact, all wireless communication standards, e.g. GSM, UTRAN, E-UTRAN, WLAN etc., clearly specify the OOB emission requirements to limit or at least reduce the unwanted emissions. Reference is made to 3GPP TS 25.101, “User Equipment (UE) radio transmission and reception (FDD)”, 3GPP TS 25.102, “User Equipment (UE) radio transmission and reception (TDD)”, 3GPP TS 25.104, “Base station (BS) radio transmission and reception (FDD)”, 3GPP TS 25.105 “Base Station (BS) radio transmission and reception (TDD)”, 3GPP TS 36.101, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); User Equipment (UE) radio transmission and reception”, 3GPP TS 36.104, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); Base station (BS) radio transmission and reception” and 3GPP TS 05.05, “Radio Transmission and Reception”. Spurious emissions requirements are defined in order to limit the emissions outside of the operating band where the UE or BS is operating They are primarily approved and set by the national and international standardization and regulatory bodies e.g. ITU-R, FCC, ARIB, ETSI etc.
Unwanted emissions are caused by a number of things, for example: harmonic emissions, intermodulation products, non-linearities and modulation artefacts.
The major OOB and spurious emission requirements are typically specified by the standards bodies and eventually enforced by the regulators in different countries and regions for both UE and the base stations. The requirements comprise of:                Adjacent Channel Leakage Ratio (ACLR)        Spectrum Emission Mask (SEM)        Spurious emissions        
The specific definition and the specified level of these requirements can vary from one system to another. Typically these requirements ensure that the emission levels outside the transmitter channel bandwidth or operating band remain several tens of dB below the transmitted signal. Emission levels tend to decay dramatically further away from an operating band but they are not completely eliminated at least in the adjacent carrier frequencies.
The UE and BS have to meet the OOB and spurious emission requirements at all transmission power levels. Therefore, the UE and BS may be subject to a Maximum Power Reduction (MPR).
For the UE the conservation of its battery power is very critical. To achieve this, it is desired that the UE has an efficient power amplifier (PA). Design of an efficient PA is often a trade-off between efficiency and emission. The more efficient the PA is the more unwanted emissions, it will normally generate. The PA is designed for certain typical operating points or configurations or set of parameter settings e.g. modulation type, number of active physical channels, e.g. resource blocks in E-UTRA or number of CDMA channelization codes code/spreading factor in UTRA. In practice, the UE may operate using any combination of modulation, physical channels etc. Therefore, in some UL transmission scenarios the UE power amplifier may not be able to operate in the linear zone, thereby causing unwanted emissions due to harmonics or other non-linear characteristics. To ensure that UE fulfils OOB/spurious requirements for all allowed UL transmission configurations the UE is allowed to reduce its maximum UL transmission power in some scenarios when it reaches its maximum power. This is known in the standards as maximum power reduction (MPR) or UE power back-off in some literature. For instance a UE with maximum transmit power of 24 dBm power class may reduce its maximum power from 24 dBm to 23 or 22 dBm depending upon the transmission configuration.
The BS may also have to perform MPR but this is not standardized, Secondly the BS can afford to have a PA with larger operating range since its efficiency is less critical compared to that of UE.
The MPR values for different configurations are specified in the standard. The UE uses these values to apply MPR when the conditions for the corresponding transmission configurations are fulfilled. These MPR values are regarded as static in a sense that they are independent of resource block allocation and other deployment aspects.
In E-UTRA for LTE, an additional MPR (A-MPR) for the UE transmitter has also been specified in addition to the MPR. The difference is that the former is not fully static. Instead, the A-MPR can vary between different cells, operating frequency bands and more specifically between cells deployed in different location areas or regions. In particular the A-MPR is applied by the UE in order to meet the so-called additional spurious emission/OOB emission requirements.
The A-MPR is specified at UE maximum output power and applies in addition to the MPR. It depends on the E-UTRA channel bandwidth, position of the RBs on which the UE transmission happens as well as the number of RBs allocated for such transmission. Different A-MPR can also be specified depending on the channel position within the operating band.
A parameter known as Network Signalling (NS) is used to signal to the UE the possibility of doing power back-off in order to fulfil certain spurious/OOB emission requirements in the cell coverage area. Reference is made to 3GPP TS 36.101, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); User Equipment (UE) radio transmission and reception”. The NS value is signalled by the BS in the broadcast message. The NS is configured by the operator. In case no specific NS is signalled, the BS will send NS_01 which indicates the UE that no back-off is allowed. In the 3GPP specifications, A-MPR is specified for each NS-value.
In the UE there is a function for determining A-MPR depending on resource block allocation, carrier frequency, etc. The specified A-MPR in the 3GPP standard is the maximum allowed power back-off to be done by the UE. However, the actual power back-off by the UE may be smaller. This is implementation dependent.
The concept of A-MPR does not exist in the UTRA standard. A restriction on the maximum output power to be transmitted by the UE can be set by the network and sent in the IE (Information Element) “Maximum allowed UL TX power”. Maximum output power can also be set by the eNB.
In LTE, the UE may be restricted to certain uplink resource blocks, sometimes called UL RB restriction. The UE spurious/OOB emissions depend on the allocation of the transmitted RBs as well as the number of RB used for the transmission. UL RB restrictions can be specified as an alternative to A-MPR to limit these emissions. It consists of restrictions regarding UL transmissions. These restrictions can be in terms of maximum number of RBs to be allocated for a UE and/or certain positions within the channel bandwidth. This is done in the eNB scheduler.
Another factor, different from OOB and spurious emissions, is human exposure to radiofrequency (RF) electromagnetic fields (EMF), which are transmitted by the UE. The guidelines on RF exposure to human are from the International Commission on Non-Ionizing Radiation Protection (ICNIRP, 1998) and from the Institute of Electrical and Electronics Engineers (IEEE, 1999). The limits in these recommendations are similar and they have been used as the basis for national standards and regulations in many countries. The ICNIRP guidelines, which are the most widely used recommendations, have been endorsed by the World Health Organization (WHO).
These RF exposure guidelines are science-based and the prescribed limits have been set with substantial safety margins. They provide protection from all established health effects from short-term and long-term exposure to RF fields, and the safety of children and other segments of the population have been taken into account.
Specific Absorption Rate (SAR) is introduced to measure impact on the human body from the exposure of RF EMF transmitted by the UE. SAR is a measure of the maximum energy absorbed by a unit of mass of exposed tissue of a person using a mobile phone, over a given time or more simply the power absorbed per unit mass. Advised by ICNIRP, the communication administration departments of different countries issued the SAR limits. For instance, the Federal Communications Commission (FCC) has determined that the SAR limit is 1.6 W/kg for cell phone. The SAR limit in Europe and in most countries is 2 W/kg.
The UE should comply with the SAR requirements or any type requirements for limiting the RF exposure to human which are specified by the regulator in an individual country, region, province or state etc. In order to meet these requirements, the UE may also have to reduce its maximum output power. Hence the UE maximum output power is limited by the SAR limit.
In prior art, a generic term called power management is also interchangeably used for controlling emissions to limit the SAR. The power management MPR (P-MPR) is the amount of UE power output power reduction to meet the RF exposure requirements.
In prior art, one or more parameters associated with the MPR to be applied by the UE to meet the SAR or any type of RF exposure requirements are signalled to the UE. This means the P-MPR may also be signalled to the UE. This is due to the fact that SAR or RF exposure requirements may vary from one region to another. Hence the amount of the MPR required by the UE to meet the requirements may vary from one cell to another.
In an FDD radio, a device known as duplexer or duplex filter is often used to connect the transmitter and receiver to the same antenna while at the same time it limits the signals from the transmitter that are entering the receiver. The interference from the transmitter the own receiver is also commonly termed as transmitter noise. The source of transmitter noise is the out of band. The duplexer substantially suppresses the transmitter noise. The duplexer also suppresses the blocking signal due to its own TX signal.
The design and implementation of a duplexer becomes more difficult depending upon various factors: wide pass band, small duplex gap, large stop-band requirements. As an example, in case of FDD 700 MHz or FDD Band 28, the pass band is very wide (i.e. 45 MHz in each direction) and the duplex gap is small. In this specific scenario, the 3GPP specifications have been specified assuming a dual duplexer implementation, where each duplexer is 30 MHz wide, see FIG. 3. Reference is also made to 3GPP TR 36.820, “LTE for 700 MHz digital dividend”.
In a TDD radio, the transmitter and receiver is not active at the same time, therefore, TX-RX isolation is not needed. However, a filter may be desirable to fulfill certain stop-band requirements.
In the 3GPP standards, various methods of signalling of information are used. A reason for signalling is to convey information from one node to another. One method is that one node sends the information explicitly and directly to another node. Another method is to send an index into table. The content of the table is specified in the standard. The receiving node has a copy of the table and by using the index as an entry into the table the information can be retrieved. The advantage is that only the index is necessary to transfer which reduces the transmitted data. With further methods, mathematical functions or algorithms are used by a receiving node and a sending node. The mathematical function or algorithm is specified in the standard, and thus known to both the sending node and the receiving node. The input data to the function/algorithm calculated by the sending node and transmitted to the receiving node. On the receiving node, the function/algorithm is used to compute the signalled information using the transmitted input data with the function/algorithm.
EP11799210 discloses signalling regarding the characteristics of the filter/duplexer implementation by a UE. Consider a scenario, in which the UE uses more than one filter/duplexer to support an operating band, which is deployed by a network. According to EP11799210, the UE may thus signal to the radio network node the number of filter/duplexers that the UE has implemented to support the operating band. Therefore, the radio network node is able to select appropriate mobility parameters. A problem may however be that the radio network node cannot ensure that the OOB emissions will be fulfilled, i.e. that OOB emissions are at or below certain levels at certain frequencies.